We're now at the part of our conversation where I can answer the question we started off with, which is, why do you breathe? And we talked about how, eh, it's oxygen and we need that. Well, oxygen is not really a fuel for metabolism.
It's needed to go through aerobic metabolism, but the fuel is coming from your fat and carbohydrates. I only need oxygen during aerobic metabolism, but I'm very effective at anaerobic, which means I can produce energy without the need of oxygen. But to finish those processes, I've got to have the oxygen around.
And so it's a little bit of a twist here. This is also explaining why even if you're an anaerobic athlete, you still care deeply about your aerobic system because this is what allows you to recover, to completely metabolize your carbohydrates, to finish that process and restore yourself back to homeostasis. The faster you can do that, the faster you can repeat your anaerobic processes.
You can recover, you can get back to training, get back to competition. The more you practice, the better you get, the better you perform. And so what's actually fully happening is this.
When you take a breath in and you inhale, you're bringing in amongst other things, but primarily oxygen. When you take a breath out, you're breathing out CO2. The oxygen you bring in is primarily there to regulate metabolic processes.
But the CO2 you're exhaling is regulating your pH. Now there's a handful of things your body will regulate almost anything else. One of them is your pH.
It does not like to mess with this. If you were to look at other markers like say your blood glucose, you realize that that's highly variable. It can be as low as, you know, 70 milligrams per deciliter, as high as 150 during exercise or something like that.
And so you can see it all double or maybe even triple the amount in the blood. You would never do that with pH. It has an extremely tight window that it will not move out of.
And that's because all the enzymes that are required for you to go through any metabolic process need to be in a certain pH range. If it gets out of that, it becomes too acidic or too alkalotic. They can't function, you can't create energy.
You're going to die very, very quickly. So pH is insanely important to hold into a tight window. And so what happens is you don't feel that air hunger or that desire to breathe because oxygen starts getting low.
Remember, especially at rest or even during exercise, you can produce energy anaerobically. So when you start getting low on oxygen, you'll just switch to anaerobic metabolism. It's not necessarily a reason for you to panic, to stress, or to change your behavior.
Increases in CO2 though will do that. And so remember your muscle is, whether it's using fat as a fuel or carbohydrates as a fuel, it's trying to generate a molecule called ATP. This is the energy currency in all of biology.
And it doesn't matter what you use that ATP for by the way. It doesn't matter if we're talking about skeletal muscle, we're talking about cardiac muscle or anything else. So whether you're using this for exercise to power your brain to recover, to digest food, it's irrelevant here, right?
We're going to use carbohydrates or fat as a fuel, we're going to make ATP. And then at the end, the final byproduct of all metabolism is going to be water, CO2, and ATP. So the CO2 concentration increases as metabolic rate increases.
As a result of that, you start then moving CO2 from your tissue into the blood. Concentrations of CO2 then and blood go up. You've got chemoreceptors in your brainstem and various other places that are going to be paying extreme attention to the amount of CO2 in your blood.
If CO2 gets really, really high, we call this hypercapnia. If it gets low, it's called hypocapnia. Remember those terms.
So hypercapnia increases in CO2 concentration actually signal your red blood cells to drop the oxygen on them, making it easier for your muscle to extract and absorb the oxygen. Effectively you think about it this way. If CO2 is high in the blood, your body is under the assumption you're going through a lot of metabolism, so it's under the assumption that we want to use and need a lot of oxygen.
So it reduces that affinity. And this is called the Bohr effect. If you get hypocapnic, again too low of CO2, it does the opposite.
Now this is going to be counterintuitive when we talk about things like CO2 tolerance and respiratory rate in future episodes as to why you could potentially have problems with hyperventilation or over-breathing. So what's happening in this context is those signals are being sent to your brain and that is interpreting it as saying CO2 is too high, let's reduce that. The way you reduce CO2 concentrations in your blood is to exhale.
And so this would cause you to increase your respiratory rate and to start either mildly or excessively hyperventilating. And this is why as you exercise your respiratory rate, again the amount of breaths you're taking, goes up. It is in part to increase and bring in oxygen, of course.
But when we're doing it anaerobically, we're not using oxygen anyways. So the real reason we're breathing so hard and we're panting, [Andy breathing deeply] and all that stuff as we're getting harder and harder of our exercise is because we're trying to dump and get rid of all that CO2 buildup. Remember, excess CO2 is altering pH.
This is making us more acidic. This becomes an extreme problem. And so another way to think about this is, when you inhale, that's actually a sympathetic driver.
And so your heart rate increases during inhalation. When you exhale, it is parasympathetic and it drops. So effectively what's happening is your body is sort of saying, oh, you're inhaling, we're assuming then you're bringing in oxygen.
Let's get prepared to deliver this oxygen throughout the system. When you're exhaling, it's the opposite. I don't want to be in a situation where I'm hyperventilating.
I don't need to be breathing too much because if again, that CO2 gets too low, instead of being acidic, we are now in respiratory alkalosis. So the opposite direction, right? We're too basic.
And so it slows the heart rate down. So every time you take a breath in, your heart rate jumps up a little bit. Every time you take a breath out, it goes down a little bit.
So if I'm altering my respiratory rate, I'm then altering my heart rate. And this is why things like HRV are so intrinsically tied to things like respiratory rate. I can't let us move off this point without saying one final thing.
I know we want to get to our three Is here in one second. But a lot of people are aware, and in the coaching world, people use HRV very often, and there's a lot of data to support this. There's a lot of critical information we can get for assessing, say, exercise volume, fatigue, readiness, and things like that.
Tons of value there. But I don't think enough people are paying attention to respiratory rate. This is really highlighted in a paper that just came out in the last few months, and so I'd like to bring this to your attention.
What they did is looked at college-aged students and they simply measured their respiratory rate. And one of the things that they found that's interesting is for every breath per minute that increase, so if a respiratory rate went from 15 breaths per minute to 16 breaths per minute, they increased their likelihood of experiencing stress by 1. 25X.
And what I found particularly interesting about this is they found that irrespective of changes in things like HRV, total hours of sleep, sleep efficiency, sleep onset, and various other things that are typically the metrics used to measure overall stress and autonomic nervous system functionality and things like that. And so what we're going over here is not to say that HRV or sleep are not good metrics to take, they clearly are. It's just that you're going to find things in the respiratory rate that you're not necessarily going to see in other places that give you great clues about overall stress.
So strongly encourage you to pay attention to respiratory rate. And we'll talk about that plenty in the future.
